In the past, platinum temperature-measuring resistance elements were commonly parts made by coiling platinum resistance wire into a coil shape and enclosing in an insulator such as ceramic, or by forming platinum resistance film and arranging on glass or the like. Specifically, elements were manufactured by bending coiled platinum resistance wire into a U-shape and then inserting through and drawing out of vertical holes in a cylindrical support member having multiple vertical holes to support a coil-shaped part in vertical holes; and by provisionally stopping the platinum resistance wire by coating one end surface of the support member with glaze, and then after filling the vertical holes with insulating powder, coating the other end of the support member with glaze and heat sealing in a furnace (for example, refer to Japanese Patent No. 2517587, FIG. 2).
Moreover, regarding elements configured by forming a platinum resistance film, a platinum thin film was formed on an aluminum substrate using a sputter or electron beam device, and after coating with resist and masking in a specified pattern, exposing to light and developing, and then removing the unnecessary resist, the platinum thin film other than the pattern was removed by dry etching or wet etching, the platinum resistance film was formed in the specified pattern by removing the resist, and a thin film type platinum temperature-measuring resistance element was obtained by covering the platinum resistance film with a protective film of glass or the like (for example, refer to Japanese Unexamined Patent Publication No. 2003-179276).
When manufacturing these platinum temperature-measuring resistance elements, normally the element is sealed with a glaze or glass frit after annealing the platinum resistance wire or platinum resistance film in a furnace, but in order to prevent contamination of the platinum resistance wire or platinum resistance film, purging is conducted inside the furnace with a mixed gas to which oxygen is intentionally added, for example, argon 85%-oxygen 15%. The small amount of oxygen in this purge gas is present in order to protect the platinum wire or resistance film from contamination, and there is no clear standard for the amount. Nonetheless, this purge gas containing oxygen remains between the aforementioned support member or the platinum resistance film and the protective film when sealing, and variations of resistance value are produced by oxidation of the platinum resistance wire or resistance film.
In the past there was no discussion of the uncertainty of the resistance value caused by this oxidation of platinum, and non-negligible resistance value variations occurred in precision temperature measurements. This is because the mechanisms of quantitative resistance value variation by oxidation-reduction of the platinum resistance wire were not understood, and there was a lack of knowledge about changes of platinum resistance wire caused by the oxygen concentration in the purge gas in the furnace during manufacturing.
Thus, in view of the previously described circumstances, in an attempt at resolution, an object of the present invention is to demonstrate the mechanisms of quantitative resistance value variation by oxidation-reduction of the platinum resistance wire, and to offer a manufacturing process to obtain a stable platinum temperature-measuring resistance element with less resistance value variation in the temperature region of use.